There are known plasma accelerators with closed electron drift (cf., "Plazmennye uskoriteli" edited by L. A. Artsimovich, 1973, The Mashinostroenie Publishers, Moscow, pages 5 to 25) comprising a discharge chamber accommodating an anode with gas distribution cavities, a magnetic system for generating in the interior of the discharge chamber a magnetic field with the lines of force thereof being transverse to the flow of gas therein at a first approximation. Provided outside the interior of the discharge chamber in proximity to its outlet section is a cathode. These accelerators can ionize and accelerate ions of various substances, and have found wide industrial application.
There is known a plasma accelerator with closed electron drift (cf., L. A. Artsimovich "Razrabotka statsionarnogo plazmennogo dvigatelya i ego ispytanie na iskusstvennom sputnike Zemli "Meteor", Kosmicheskie issledovania, 1974, issue 3, pages 451 to 459). This plasma accelerator comprises a discharge chamber with a housing including coaxial inner and outer cylindrical elements defining an annular acceleration passage open at the side of the outlet section of the discharge chamber. The acceleration passage accommodates a hollow anode communicating with a gas feeding system through at least one inlet passage and with the accelerating passage by way of outlet passages. The accelerator also comprises a magnetic system with pole pieces of which one embraces the outer cylindrical element and the other is positioned in the inner cylindrical element, and a cathode located outside the interior of the discharge chamber near to its outlet section.
These known accelerators operate efficiently on a range of easy-to-ionize gases with a relatively low ratio of ionization potential .phi..sub.i to the mass M of ions at substantially high flow rates of the working gas. Such working gases include primarily vapours of alkali metals or for example, xenon. However, when operating on xenon at low flow rates of gas, as well as when operating on argon, nitrogen, oxygen and other gases, the performance of the accelerator is low because of difficulties associated with meeting a major condition for efficient operation, viz.: EQU .lambda..sub.u .ltoreq.L.sub.k, (1)
where
.lambda..sub.u is the free travel path of atoms prior to ionization, and PA1 L.sub.k is the length of the discharge chamber as measured from the anode to its outlet section.
In addition, efficiency is further lowered due to a jump in anodic potential caused by reduced concentration of plasma in the entire passage and reduction in the magnitude of electron flow N.sub.e to the anode due to thermal motion (N.sub.e =1/4 n.sub.e v.sub.e, where n.sub.e is the concentration and v.sub.e is the thermal velocity of electrons). An increase in the anodic potential jump .phi..sub.a leads, in particular, to contraction of the discharge whereby it tends to penetrate to the outlet passages of the anode and to the interior of the anode. Ions generated inside these passages are neutralized at the walls of the anode, and therefore the amount of energy expended for ionizing the gas in the discharge chamber is increased.